Oxide materials such as aluminas, titanias, and zirconias are used as catalyst supports in a wide range of industrial processes, including the Fischer-Tropsch synthesis of hydrocarbons. The catalyst support provides a surface over which the catalytically active material is dispersed. The catalyst support may also confer other properties on the catalyst, such as its physical and chemical stability.
In order to adapt properties, such as solubility, it is known to coat support materials with silica. This may be done by applying a silicon compound to the surface of the support material, followed by drying and calcining to decompose the silicon compound and leave silica deposited as a coating on the catalyst support.
WO 99/42214 describes a method of treating a catalyst support comprising introducing onto and/or into an untreated catalyst support, which is partially soluble in an aqueous acid solution and/or a neutral aqueous solution, Si, Zr, Cu, Zn, Mn, Ba, Co, Ni and/or La as a modifying component. In the Examples, silica modified alumina and titania materials were made by adding alumina or titania to ethanol solutions of tetraethyl-orthosilicate (TEOS), holding the resulting mixture at 50-75° C. for one hour before drying under vacuum at 95° C. and calcining at 500° C. to decompose the silicon compound.
We have found a drawback of merely applying an alkyl silicate followed by drying and calcining, is that a considerable amount of the alkyl silicate, up to 50% in some cases, may be lost from the support during the process by evaporation. This results in equipment fouling and represents an inefficient waste of a valuable raw material, as well as resulting in an inconsistent product quality.